The present invention relates to refining elements for use in disk-type refiners for working, i.e. for defibering, refining or dispersing lignocellulosic fiber material in the form of chips or pulp. The working of the lignocellulosic material can have the purpose to manufacture, for example, recycled fiber pulp or mechanical pulp, such as thermomechanical pulp (TMP) and chemi-thermomechanical pulp (CTMP). More particularly, the present invention relates to a pair of cooperating refining elements, which are intended to be positioned directly in front of each other on opposed refining disks in a refiner of this kind.
The working of fibrous material takes place in the refining gap formed between the refining elements on two opposed refining disks rotating relative to each other. The fibrous material is thereby subjected to mechanical action by working means on the refining elements, while it simultaneously moves by the effects of centrifugal force. The working means can be formed as continuous or discontinuous bars, teeth or in some other manner.
During the defibering of fibrous material in the form of chips, it is desired for the chips to be disintegrated to individual fibers with a minimum of fiber shortening. Experiments have proved that the configuration of the refining elements in the inner portion of the refining gap is of great importance for the feed of the material through the refining gap as well as for the defibering process. During the dispersion of recycled fiber pulp, working is desired which does not cause any fiber shortening or reduction in the freeness value (CSF) of the pulp.
Working, which causes fibrillation and fiber shortening, occurs most often when the refining means are formed with bars, by the effect of the edges of the bars. Conventional refining elements with working means in the form of bars with intermediate grooves can also result in a non-uniform flow of the material through the refining gap. This results in the load on the motor or motors driving one or both of the refining disks being uneven.
As a result thereof, the process will be difficult to control, and the energy consumption increases. It can also effect the quality of the worked pulp.
These and other difficulties in the prior art have now been alleviated by the invention of apparatus for refining lignocellulosic material comprising a first refining element including a first refining surface, and a second refining element including a second refining surface facing the first refining surface thereby providing a refining gap therebetween, the first and second refining surfaces being relatively rotatable with respect to each other whereby the lignocellulosic material can be refined while passing through the refining gap, the first refining surface including a first plurality of rows of projecting working pins having a substantially circular cross-section and at least one first strip projecting above and extending substantially circumferentially along the first refining surface, and the second refining surface including a second plurality of rows of projecting working pins having a substantially circular cross-section and at least one second strip projecting above and extending substantially circumferentially along the second refining surface, the first and second pluralities of rows of projecting working pins disposed at selected radial positions on the first and second refining surfaces whereby the first and second pluralities of rows of projecting working pins avoid contact with each other upon the relative rotation of the first and second refining surfaces. In a preferred embodiment, the first and second pluralities of rows of projecting working pins are disposed at alternating radial positions with respect to each other.
In accordance with one embodiment of the apparatus of the present invention, the at least one first strip comprises a plurality of first strips and the at least one second strip comprises a plurality of second strips.
In accordance with another embodiment of the apparatus of the present invention, the first and second pluralities of rows of projecting working pins are substantially cylindrical, and include a rounded upper surface distal from the first and second refining surfaces.
In accordance with another embodiment of the apparatus of the present invention, the at least one first and second strips are disposed along an arc. Preferably, the at least one first and second strips are disposed adjacent to the first and second pluralities of rows of projecting working pins on the first and second refining surfaces.
In accordance with another embodiment of the apparatus of the present invention, the at least one first and second strips extend continuously across the entire first and second refining surfaces.
In accordance with another embodiment of the apparatus of the present invention, the at least one first and second strips extend discontinuously across the first and second refining surfaces.
In accordance with another embodiment of the apparatus of the present invention, the first and second refining surfaces each includes an inner radial portion and an outer radial portion, the first and second plurality of rows of projecting working pins on the at least one first and second strips being disposed on the inner radial portions of the first and second refining surfaces. Preferably, the apparatus includes working means for the lignocellulosic material disposed on the outer radial portions of the first and second refining surfaces. In a preferred embodiment, the working means comprises a plurality of radially projecting bars.
The present invention offers a solution to the above problems. Opposed cooperating refining elements are provided with projecting working means in the form of pins with a circular cross-section. The pins on one of the refining elements are arranged to extend into the interspace between the pins on the opposed cooperating refining element. The refining elements are also provided with flow restrictions in the form of strips extending substantially in the circumferential direction.